1. Field of the Invention
The present invention relates to a process for providing protective coatings on the surfaces of a material of aluminum or an aluminum-based alloy which is molded in shaped sections by extrusion.
2. Prior Art
According to conventional procedures for providing protective coatings on the surfaces of a material made of aluminum or an aluminum-based alloy (hereinafter referred to as an aluminum material) molded in shaped sections by extrusion in a molding plant, the aluminum material is cut in desired lengths and the thus cut pieces, optionally, after having been subjected to thermal aging or annealing, are cooled to room temperature and stored in the same molding plant. Then the materials are moved to a surface-treating plant where coating operations by a chemical oxidation method, anodic oxidation method, immersion coating, electrodeposition, or the like are carried out.
The above conventional process is economically disadvantageous because of its stepwise complexity, and because it requires operational facilities of a large scale and because of difficulties in process control, as well as because of its large consumption of electricity, steam, compressed air and fuels.
The conventional process tends to cause further difficult problems from the standpoint of economy, safety or environmental pollution. In the coating method which is a wet process carried out by use of aqueous coating materials, it is inevitable to spend very much money on the disposal of sewage or waste water, not to mention that the supply of large quantities of good quality water is required. When coating materials like paints, varnishes and lacquers are used, it is difficult to avoid the problems of fire hazards and explosion, air pollution, damage to workers' health, and the like, which may be caused by the presence of organic solvents contained in large quantities in the coating materials.
Furthermore, the quality of the coating films obtained by the conventional method generally has been found to be unsatisfactory, due to the fact that aluminum and aluminum-based alloys have a rather poor affinity with the conventional coating materials.